OpenGL (Introduction - glBegin & glEnd)

#ifdef WIN32
#include <windows.h>
#endif

#include <stdlib.h>
#include <iostream>
#include <fstream>

#ifdef __APPLE__
#include <GLUT/glut.h>
#include <OpenGL/gl.h>
#include <OpenGL/glu.h>
#else
#include <GL/glut.h>
#include <GL/glu.h>
#include <GL/gl.h>
#endif

char flag;
void display(void)
{
    /* bersihkan layar dari titik pixel yang masih ada */
    glClear (GL_COLOR_BUFFER_BIT);
    glColor3f (0.5, 1.0, 0.0);

    /* gambar 5 titik di layar */
    //glBegin(GL_POINTS);
    //glBegin(GL_LINE_STRIP);
    //glBegin(GL_LINE_LOOP);
    //glBegin(GL_LINES);
    //glBegin(GL_TRIANGLES);
    //glBegin(GL_TRIANGLE_FAN);
    //glBegin(GL_TRIANGLE_STRIP);
    //glBegin(GL_QUADS);
    //glBegin(GL_QUAD_STRIP);
    //glBegin(GL_POLYGON);

    //kotak2x2
    glColor3f (0.3, 0.3, 0.3);
    glBegin(GL_POLYGON);
    glVertex3f (0.0, 0.0, 0.0);
    glVertex3f (0.0, 0.8, 0.0);
    glVertex3f (-0.8, 0.8, 0.0);
    glVertex3f (-0.8, 0, 0.0);
    glEnd();
    glBegin(GL_POLYGON);
    glVertex3f (0.0, 0.0, 0.0);
    glVertex3f (0.0, -0.8, 0.0);
    glVertex3f (0.8, -0.8, 0.0);
    glVertex3f (0.8, 0, 0.0);
    glEnd();
    glColor3f (0.7, 0.7, 0.7);
    glBegin(GL_POLYGON);
    glVertex3f (0.0, 0.0, 0.0);
    glVertex3f (0.0, 0.8, 0.0);
    glVertex3f (0.8, 0.8, 0.0);
    glVertex3f (0.8, 0, 0.0);
    glEnd();
    glBegin(GL_POLYGON);
    glVertex3f (0.0, 0.0, 0.0);
    glVertex3f (0.0, -0.8, 0.0);
    glVertex3f (-0.8, -0.8, 0.0);
    glVertex3f (-0.8, 0, 0.0);
    glEnd();
    glLineWidth(500);
    //mulai huruf A
    if(flag=='a'){
    glColor3f (1, 1, 1);
    glBegin(GL_LINE_STRIP);
    glVertex3f (0.0, 0.7, 0.0);
    glVertex3f (-0.4, -0.1, 0.0);
    glVertex3f (0.4, -0.1, 0.0);
    glVertex3f (0.0, 0.7, 0.0);
    glEnd();
    glBegin(GL_LINE_STRIP);
    glVertex3f (-0.4, -0.1, 0.0);
    glVertex3f (-0.7, -0.7, 0.0);
    glEnd();
    glBegin(GL_LINE_STRIP);
    glVertex3f (0.4, -0.1, 0.0);
    glVertex3f (0.7, -0.7, 0.0);
    glEnd();
    }
    //mulai huruf I
    else if(flag=='i'){
    glColor3f (1, 1, 1);
    glBegin(GL_LINE_STRIP);
    glVertex3f (-0.2, 0.7, 0.0);
    glVertex3f (0,0.7,0);
    glVertex3f (0.2,0.7,0);
    glEnd();
    glBegin(GL_LINE_STRIP);
    glVertex3f (0, 0.7, 0.0);
    glVertex3f (0, -0.7, 0.0);
    glEnd();
    glBegin(GL_LINE_STRIP);
    glVertex3f (-0.2, -0.7, 0.0);
    glVertex3f (0,-0.7,0);
    glVertex3f (0.2,-0.7,0);
    glEnd();
    }

    //mulai huruf E
    else if(flag=='e'){
    glColor3f (1, 1, 1);
    glBegin(GL_LINE_STRIP);
    glVertex3f (0.3, 0.7, 0.0);
    glVertex3f (0,0.7,0);
    glVertex3f (-0.3,0.7,0);
    glEnd();
    glBegin(GL_LINE_STRIP);
    glVertex3f (0.3, 0, 0.0);
    glVertex3f (0,0,0);
    glVertex3f (-0.3,0,0);
    glEnd();
    glBegin(GL_LINE_STRIP);
    glVertex3f (0.3, -0.7, 0.0);
    glVertex3f (0,-0.7,0);
    glVertex3f (-0.3,-0.7,0);
    glEnd();
    glBegin(GL_LINE_STRIP);
    glVertex3f (-0.3, 0.7, 0.0);
    glVertex3f (-0.3,-0.7,0);
    glEnd();
    }

    //mulai huruf O
    else if(flag=='o'){
    glLineWidth(1000);
    glColor3f (1, 1, 1);
    glBegin(GL_LINE_STRIP);
    glVertex3f (-0.3, 0.6, 0.0);
    glVertex3f (0.3,0.6, 0);
    glVertex3f (0.3,-0.6,0);
    glVertex3f (-0.3,-0.6,0);
    glVertex3f (-0.3, 0.6, 0.0);
    glEnd();
    }
    //mulai huruf U
    else if(flag=='u'){
    glColor3f (1, 1, 1);
    glBegin(GL_LINE_STRIP);
    glVertex3f (-0.4, 0.6, 0.0);
    glVertex3f (-0.4,-0.6, 0);
    glVertex3f(0.4,-0.6,0);
    glVertex3f(0.4,0.6,0);
    glEnd();
    }
    glFlush ();
}

void kunci(unsigned char key, int x, int y)
{
    switch (key)
    {
            /* aplikasi berhenti ketika tombol q ditekan */
        case 27 :
        case 'q':
            exit(0);
            break;
        case 'a':
            flag='a';
            break;
        case 'e':
            flag='e';
            break;
        case 'i':
            flag='i';
            break;
        case 'u':
            flag='u';
            break;
        case 'o':
            flag='o';
            break;
    }
    glutPostRedisplay();
}

int main(int argc, char *argv[])
{
    glutInit(&argc, argv);
    glutInitWindowSize(400,400);
    glutInitWindowPosition(100,100);
    glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);
    glutCreateWindow("Primitif");
    glutKeyboardFunc(kunci);
    glutDisplayFunc(display);
    glutMainLoop();
    return 0;
}